A couple of years ago I was gifted one of the smaller, 1.08 venturi Autolite 4100 carbs but never got around to dicking with it. It came off, according to the tag, a '66 Thunderbird with a 390.

Besides a kit I got an electric choke conversion for it which doesn't seem to work all that well but being in Texas I've now got about eight months to figure it out.

I haven't messed with the 4100 mostly because the Edelbrock runs really well.

As is the 4100 runs better. Off idle is smoother. It feel cleaner all around. I didn't drag out the O2 sensor yet but it did smell a bit rich after enough third gear heavy foot to get into the secondaries.

Off idle may be a little smoother because it's idling a one to two hundred rpm higher than the old carb. It's certainly easier to lug it off the line from stop signs.

Definitely to be continued. I can see why these things have such a good reputation. So simple and so smooth.

 

The 4100 is a great carb.

Are you sure it came off a 390? The 390's usually had the big 4100 not the small one.

 

Ford put the 1.08 on big blocks for emissions. They are commonly found on ford big blocks of the era. However, the bb 1.08 is calibrated differently than the sb 1.08's.

I like how the primary venturi are smaller than the secondary venturi.

I have a good thread about them. The problem with them is that they are 40+ years old and finding one that hasn't had the boosters or throttle shafts changed is very difficult.

 

According to the folks at "Mustang Tech", the 1966, 390, thunderbird used the 4100 4V with 1.08" venturi, rated at 480 CFM, carburetor.

This carburetor just might work on the 300, keeping the secondaries out of the equation.

The 1966 289 Mustang used the same carburetor!

 

No, that is not true. Just because you have two 1.08's side by side doesn't make them the same. Ford stamped the throttle side toe of each 4100 to stipulate on what engine it was installed. The booster clusters were different from a 1.08 destined for a 289 than those for a 390 or 428, as were the internal passages drilled in the body. Different serial numbers mean different application, which means different calibrations. They may look the same but the differences are internal, hence the different numbers.

For example: You have the 1.08 C6FS-C, calibrated for a 390 or 428 with a C6 trans, and the 1.08 C6ZF-A, calibrated for 289 mustang or Fairlane with a manual trans. Both are 1.08's, but calibrated differently.

The only 1.08 used across the boards, installed by dealerships as a service warranty replacement, was the C6PF-H, installed on 289's, 390's, and 428's. Did they every run correctly? I doubt it. Will a big block 4100 with 1.08 venturi run well on a 300? My experience said no. The sb model was a different story.

Caution with ebay 4100's. Because of mustang restorers and Pony carbs tooting the horn about the annular fuel discharge boosters of the 4100's, the price of them has risen dramatically in the past years. That being the case, many rebuilders are mixing and matching parts, boosters, throttle shafts, etc., making those carbs nightmares to tune. Also, with a 40+ year old carb the throttle shaft housings get worn and wobble, creating a wonderful air leak, vacuum leak which will test your sanity. After 40 + years things get plugged, bent, warped and tweaked, even drilled.

After playing with many 4100's I found that the annular fuel discharge boosters are nice, but don't produce any more mpg than a holley. Unless you can find a pristine 4100, don't bother. All the agro of chasing down minor problems caused by 40+ year old tiny parts caused innumerable headaches. BVA, if you got a good one, that is fantastic. Run with it. Is it idling fast b/c it is calibrated for 2 more cylinders, more flow, maybe. I hope it works for ya. Good luck.

Raven--if you want a 4v whose secondaries don't open, then use a 2v. The Autolite 2100 is the primary side of a 4100.

 

Raven, based on an admittedly brief (ten minutes around the neighborhood) test drive it works on a 300 with the secondaries in the equation.

I'm interested in seeing the AFR mapped out. It feels rock steady. There's no surge where the PV should be kicking in and there was no surge as the secondaries came on. It just pulls steady from off idle through and beyond my usual shift points.

As is I'm keeping it over the Edelbrock. If it can be made better with a bit of tuning there's no going back.

The carb is supposed to be original, but who knows? I imagine the idle speed is linkage or throttle plate related. Entirely possible I fubared something there. Assuming a jet or PV change this weekend I'll give it a good going over. Anyway, a higher idle isn't necessarily all bad with the manual transmission. I'm pretty sure with a little tinkering it will drop, though. Then I'll need to get a dashpot.

 

Appeared the 1966 390 and 289 used the same basic 1.08" venturi, 480 CFM carburetor.
Understand the 390 carburetor are stamped C6AF, C6OF & C6SF, while the 289 mustang carburetor is stamped C6ZF.
While the factory replacment generic for the 289,352 & 390 is stamped C6PF.
Seems like a whole bunch of variations for one model year.

So does the C6ZF used on the 289 work better for the 300 or the C6AF,C6OF, C6SF used on the 390?

How does off the shelf generic Edlebrock 500 compare to the C6ZF or C6AF/C6OF/C6SF series.

 

My experience is the Eddy is bolt on and play. Best mpg is the sb 1.08, by far. The magic letter in C6ZF is the Z. That stipulates a mustang, and that alone usually makes the price go up on ebay.

Yes, they are great carbs or two companies would not have copied them. Holley paid ford to use the design, and now Summit is making them. I have one.

I may of had bad luck with parts being mixed and matched on the bb 1.08's I tried. BVA seems to like his.

Good luck.

 

Any time you install an aftermaket carb on an engine it's a game of maybe. It will probably need some degree of tuning but it may run fine or good enough.

Factory engineers spend hours dyno testing engines to get ideal specs for the carb. Once you swap on a 4v intake it's a crapshoot.

The Edelbrock 500 ran out of the box but needed a rod change and a different pair of step-up springs to run pretty good. It needed secondary jets to run better. About as well as I could expect. I only dusted off the 4100 because I'm breaking in a new engine soon and figured to see how three or four different carbs look on the dyno.

The 4100 drives nicer as it sits so I am curious to check the AFR. Any carb running that smooth has to be rich.

Good 4100 cores are getting tougher to find so finding a Mustang-specific one will require some patience or plenty of extra cash. I would rather have a decent, original 1.12 600 cfm than a ratty, possibly mismatched 1.08 with a Z on the possibly original tag.

I got this one for free because I wasn't in a hurry. A friend who knows a little about carbs knew I was looking for one picked it up and gave it to me. Dumb luck it was a 1.08.

Find a reasonably priced 4100 core - either 480 or 600 cfm - and invest the extra you'd spend for a Mustang carb in a wideband O2 sensor. Then drive, take notes, and tune. No worries.

 

4100 notes:

A dashpot came on 4100's that were attached to engines with an auto trans, not manuals.

Never go by the tag. Always check the left toe on throttle side for serial numbers.

Short coming of 4100 rebuilds is there is no guide or catalog for the booster cluster numbers, showing what carb was for what engine/car, and what the booster numbers were. Air bleeds, squirters are all contained in the booster assembly.

The Summit Racing 600 cfm is a copy of a 4100, with a holley secondary diaphram and holley choke, and center hung holley floats, and screw in air bleeds. The boosters interchange with a 4100. It is an Autolite made by Holley for Summit.

 

[quote=BaronVonAutomatc;14202302 Find a reasonably priced 4100 core - either 480 or 600 cfm - and invest the extra you'd spend for a Mustang carb in a wideband O2 sensor. Then drive, take notes, and tune. No worries.[/quote]

After trying 4 4100's, I'd say to get a Holley 1848, 465 cfm. It is made for small v8's, and you can get them new, not 40 years old, on ebay for $300. It is a new carb returned to Holley under warranty and rebuilt by Holley.

I'm not trying to make light of BVA's choice. The 4100 is great--if you can find a pristine specimen.

 

Caveat emptor for sure but I'd wager most 4100 cores on the private market are pretty much original save perhaps a rebuild kit. A remanufacturer would have more capability and incentive to mix and match parts, though. But I wouldn't shy away from a reputable 4100 builder.

A decent 4100 core shouldn't be any more than a used Edelbrock or Holley. As long as you're not in a hurry you can find a good one at a fair price. Again, I wouldn't sweat whether it's a 480 or 600 cfm or what engine it came off as long as it was a complete rebuildable core.

 

If the Summit Racing 600 is a copy of the Motorcraft 4100, then the Summit must have a 1.12" venturi rather than a 1.08" venturi, right?

If I ask enough stupid questions .. will learn something about carburetors.
Always liked carburetor over EFI because of the physics associated with the carburetor.

I flunked fluid mechanics the first time at CAL Berkeley, but passed the second time around.

delta P ~ flowed squared.. through an orfice or venturi, simplified equation. So, if the compressable fluid, air, is drawn through the venturi from the pistons, pressure drop ~ cfm squared. That's the reason the 2 BBl is rated square root of 2 > 4 BBL.
Reduction in pressure below atmospheric pressure in the venturi draws liquid fuel through the orifice(jet), where the flow is ~ sq root of pressure below atmospheric.
So, theoryically the fuel flow should be directly proportional to air flow for the proper stoichiometric air/fuel mixture over a range of air flow ~ engine rpm.
The main problem is the air is compressable and the fuel is incompressable and follow different laws of physics.

Here is the problem with carburetors. The fuel flow is not direclty proportional to air flow over the entire range of engine rpm. The carburetor can be tunned for nearly constant air/fuel mixture ratio over only a limited useable rpm range.

Then if carburetor is set up at sea level by changing the jet orifice size and venturi size, then go to higher elevation above 3000 ft.,
the air/fuel mixture is too lean and melts the pistons. This happed to my 1985 Bronco 351W with stock 4BBL Holley.

Carburetors are still more fun than EFI.

 

Yes and no. Each serial number is different and calibrated differently. You are not putting it on the engine/vehicle it is intended for, so your tuning will be working around what it is designed for. I would start close to where you want to be, meaning: chose a carb calibrated for an engine near as possible to the c.i. of yours. Yeps, a 1.08 is the better choice, IMHFO. Tak shal du ha'.

 

I wanted to mention a few things about the 4100: The first is that there is a third size not many people are aware of. Ford made a 1.19 in either iirc, 57 or 58. It is a monster carb. If we say the 1.08 is 480 cfm and the 1.12 is 600, then we see that for every 1/100 of an inch the venturi is enlarged the cfm goes up 30 cfm. Therefore we can take an educated guess and say the 1.19 4100 is 810 cfm.

Another point: I have read many places on forums that the 4100 does not like heat sink and reacts poorly to it. It is quite common to find the bowls half empty on a start up. Could that be why ford made a coolant flow through spacer between the intake and the carb?